Difference between revisions of "Hydrological Analysis Using Whitebox Geospatial Analysis Tools"

From CUOSGwiki
Jump to navigationJump to search
 
(96 intermediate revisions by 3 users not shown)
Line 1: Line 1:
==Purpose==
==Introduction==
[[File:WhiteBox.png |200px]]
The purpose of this tutorial is to guide the user through the process of analyzing the hydrology of an area based on the local elevations.
This tutorial uses the opensource software Whitebox Geospatial Analyst Tools and explores some of the most useful of the hydrology tools included in it.
The intent of this tutorial is for the user to understand the process underwent, an to be able to build off of it for their specific purposes.


This tutorial uses Whitebox tools, an open source GIS software that was developed within the Center for Hydrogeomatics in Guelph University. As a result this software package has a heavy focus on hydrological analysis. For this reason Whitebox was chosen for this tutorial on hydrological analysis. WhiteBox has recently been completely re-written from the ground up using a more advanced backend. This means that the toolset has migrated away from a stand-a-lone software. It is now accessible either through code (Python or R) or as a package using QGIS. This tutorial originally used the older version but has been updated to use the QGIS version in October 2026.
This tutorial assumes that the user has some experience with GIS software.


The area of focus in this tutorial is Calabogie Ontario. This location was chosen because the Calabogie peak adds some relief to the area, and the author knew it well enough to tell if there were any errors that occurred during the analysis process.
==Introduction==
[[File:WhiteboxVersion.png|center]]
'''''QGIS is a free open source geographical information system application that has geographical viewing, editing and analyzing capabilities. Within QGIS are tools called [https://plugins.qgis.org/ "Plug-ins"]. Plug-ins are essentially developed geoprocessing features made by the QGIS developers as well as independent users who would like to expand and contribute to the functionality of the software. One particular plug-in extension found in QGIS is the Processing toolbox extension. The Processing toolbox extension is similar to the features that are found in ArcMap’s ModelBuilder. Processing is an efficient application that is capable of creating, editing and managing geographical models. The user is able to connect together workflow diagrams that involve a series of geoprocessing algorithms. For the purposes of this tutorial, a workflow will be created using geographical data of [http://en.wikipedia.org/wiki/Carp,_Ontario Carp, Ontario] in order to create a [http://en.wikipedia.org/wiki/Digital_elevation_model digital elevation model (DEM)]. This will then be used to create the slope, hillshade and aspect maps.'''''


This tutorial uses a single input, a Digital Elevation model, and produces a multitude of outputs from it, adding information that could be used for future analysis. The process that will be undergone in this tutorial is displayed in the image below. To understand the context of each tool used in this tutorial please refer back to this image as needed.
This tutorial was also done as a partial requirement of Carleton University's Advanced Topics in Geographic Information Systems 4008 course.


[[File:Overview.PNG|800x400px]]
The process that will be undergone in this tutorial is displayed in the image below. To understand the context of each tool used in this tutorial please refer back to this image as needed.

[[File:Overview.PNG|700px]]
==Data Acquisition==
In this tutorial the only necessary layer is a Digital Elevation Model (DEM) file of your area of interest. In this tutorial we are focusing on Calabogie, ON. It is recommended that you use tthis same dataset for following along.

It can be acquired and downloaded [https://www.dropbox.com/s/gd19qoa0bgqmue3/DEM.tif?dl=0 here].


==Data==
In this tutorial the only necessary layer is a Digital Elevation Model (DEM) file of your area of interest. In this tutorial we are focusing on Calabogie, ON. It is recommended that you use tthis same dataset for following along. It can be acquired and downloaded [https://www.dropbox.com/s/gd19qoa0bgqmue3/DEM.tif?dl=0 here].
A sample of this data is shown bellow.
A sample of this data is shown bellow.


[[File:DataExa.PNG|700px]]
[[File:DataExa.PNG|600px]]


For the event that the dropbox link has become inactive the process of obtaining this data is described below to make this tutorial relevant for longer.
For the event that the dropbox link has become inactive the process of obtaining this data is described below to make this tutorial relevant for longer.

Access the Government of Canada Geospatial Data Extraction Application [http://maps.canada.ca/czs/index-en.html here].
Access the Government of Canada Geospatial Data Extraction Application [http://maps.canada.ca/czs/index-en.html here].


Line 32: Line 31:
The map extent on the right side of the web page should now match the image below.
The map extent on the right side of the web page should now match the image below.


[[File:MapExtent.PNG]]
[[File:MapExtent.PNG | 600px]]




Under “Select Data to be extracted” Select “Elevation – Digital elevation model”.
Under “Select Data to be extracted” Select “Elevation – Digital elevation model”.

Under “Select options and submit job” fill all of the required boxes so that it matches the figure below. Make sure to enter the email address that you would like to have the file sent to in the “Email Address” field.
Under “Select options and submit job” fill all of the required boxes so that it matches the figure below. Make sure to enter the email address that you would like to have the file sent to in the “Email Address” field.


[[File:SelectOptions.PNG]]
[[File:SelectOptions2.png | 300px]]


An email will be sent to the entered email address shortly which contains a URL for the direct download of the data.
An email will be sent to the entered email address shortly which contains a URL for the direct download of the data.


If neither of these options are available, any DEM in a tiff format can be used.
If neither of these options are available, any DEM raster can be used.


==Acquiring and Installing Whitebox 3.4.0==
==Acquiring and Installing Whitebox Plugin (QGIS)==
Please note the previous version of Whitebox used for this tutorial is now [https://github.com/opengeos/whiteboxR/issues/138#issuecomment-4545971338 deprecated] and has transitioned to be used via coding APIs or QGIS only. This tutorial will now use Whitebox Geospatial Analysis Tools in QGIS instead of the older version. This tutorial presumes the user has some QGIS knowledge and already has QGIS installed. For more details, please see the the [https://qgis.org/download/official QGIS download page] for more instructions.
Whitebox version: 3.4.0 (The current version of Whitebox as of 2017 is 3.4.0 and this was the version used for this tutorial. A list of the download links for Windows, Mac and Linux platforms can be found [http://www.uoguelph.ca/~hydrogeo/Whitebox/download.shtml here].)


To setup your QIGS workspace for WhiteBox you will need to install the "WhiteBox Workflows for QGIS" plugin.
After the correct .zip file has been downloaded and extracted to your directory of choice the installation process is complete.


To start, find the plugin manager in QGIS by going to plugins > Manage and Install Plugins...
It is important that your machine has version 8 or higher of the Java SE Runtime Environment before trying to run Whitebox. This can be acquired [http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html here]


[[File:Plugin installer.png|400px]]
==Getting Started==


Then search all plugins for "WhiteBox Workflows for QGIS"
===Launching Whitebox 3.4.0===
After the file has been extracted the contents should look similar to the image below


[[File:FileContents.PNG]]
[[File:Install Plugin Whitebox.png|400px]]


Install the plugin, once that is finished please move on to the next section.
Double click on the "WhiteboxGIS.jar" file in order to launch the program.


==Getting Started==
'''Note:''' If you are running Windows 10 on your computer you may need to double click on the "Whitebox.bat" file to launch it instead.
===Accessing WhiteBox Tools===
You're now all set to start using WhiteBox Tools. If you do not see them go to Processing > Toolbox to display the window.


[[File:Toolbox location.png|400px]]
=== Setting up a working Directory ===
For this Tutorial I created a working directory before starting any analysis processes. This step is not necessary, though it will aid in the organization of this project.
Create a folder called "WhiteboxTutorial", or something similar.
Within this folder create one folder called "Data", and another called "DataProducts"


You will find the whitebox tools displayed at the bottom of the list. These tools will be used for the rest of the tutorial so please make sure you have access to them as shown here.
The final product will look like the image below.


[[File:WorkingDirectory.PNG]]
[[File:Whitebox in toolkit.png|500px]]
===Import DEM into QGIS===
Import the DEM you downloaded into QGIS by adding it as a layer. You can do this by finding the layer in the QGIS browser or simply dragging it from the directory into QGIS. If it correctly imported, you should see the DEM displayed on the screen.


[[File:DataExa.PNG|600px]]
Place the DEM.tif data file into the "Data" folder.
All files created from the DEM file will be placed in the "DataProducts" folder. i.e. all files output by Whitebox tools while going through this tutorial.
Also, project files will be saved directly within the "WhiteboxTutorial" folder itself.


==Hydrological Analysis==
===Adding Elevation Data and Saving the Map Project===


To add the elevation data to the project select the icon in the top left of the Whitebox window, highlighted in red in the image below. (or use the hotkey Ctrl + L)


===DEM Pre-Processing===
[[File:AddData.png]]


Pre-processing is an important first step in any hydrological analysis as this process identifies and corrects all features within the DEM that may disrupt the flow analysis. Since all products are derived from the DEM it is important to make these corrections at the begging of the process to prevent these errors from carrying through into all of the hydrological outputs.
A popup window will then appear.
In this window navigate to the location of the Calabogie DEM data file and select open.


In this tutorial the "Fill Depressions" tool is used to hydrologically correct the DEM. This was chosen because it is much more computationaly efficient than any of the breach tools, finishing much quicker.
[[File:AddDEM.PNG]]


You will likely recive a popup message like the one below.
This tool is found in the location below.
Select okay to add your data to the map.


[[File:ErrorMsg.PNG]]
[[File:Fill depressions tool location.png]]


The dialog box that appears for this tool is shown below. The input file should be set to the original Calabogie DEM.


[[File:Fill depressions tool.png|600px]]
To save your project select "Save Map" under the "Cartography" tab. (or use the hotkey Ctrl + S)


The output of this tool is shown below. It does not appear very different to the original DEM, but will closer inspection differences within the areas identified in the Find No-Flow Cells output can be seen.
[[File:SaveMap.png]]


[[File:FillDepressionsOtp.PNG|600px]]
In the pop up window that appears navigate to the location that you would like to save the project and select "Save".


===Flow Pointer===
[[File:SaveLoc.PNG]]


A flow pointer tool in Whitebox is a tool that identifies which area surrounding a cell is the lowest. The value of this cell is then assigned corresponding to the relative direction of this area. This information is not too useful on its own, but it is used as an input to many other hydrology tools because it denotes the direction that water will flow from each cell.
You should now be ready for analysis.


Whitebox has many different flow pointer tools that each use a different method to produce their results.
==Hydrological Analysis==
In this tutorial "D8 Flow Pointer" was used because many of the tools in the "Watershed Tools" toolset will only work with the output from the D8 Flow Pointer as an input.
Now that our preparation has been completed we can move on to the analysis section of this tutorial.
This tool is found in the location shown below.


[[File:D8 flow tool location.png]]
===DEM Pre-Processing===


The dialog box for this too is shown below. The input DEM raster file should be set to the output from the Fill Depressions tool.
Pre-processing is an important first step in any hydrological analysis as this process identifies and corrects all features within the DEM that may disrupt the flow analysis. More confidence can be put in the output of all future hydrological analysis with this data due to these corrections.


[[File:D8 flow tool.png|600px]]


The output from this tool is displayed below. This image contained 8 colours corresponding to the 8 directions of flow. This image appears chaotic, but will be used in other tools to create more informative data products.


[[File:FindNoFlow.PNG]]
[[File:FlowPointerOtp.PNG|600px]]


===Flow Accumulation===
[[File:FindNoFlowMsg.PNG]]


Flow Accumulation tools analyze the magnitude of cells that pour into or through an area.
[[File:FindNoFlowOtp.PNG|800px]]
This is useful on its own, allowing us to determine the relative flow through areas by comparing values of the output, and is also used as an input for many other analyses.


In this tutorial the "D8 Flow Accumulation" tool was used, as this was the one that corresponded to the D8 Flow Pointer output that was created with the previous tool.
In this tutorial the "Fill Depressions"
This tool is located in the location displayed below.


[[File:Fill.PNG]]
[[File:D8 accumulation tool location.png]]


The dialog box for this tool is displayed below. The input D8 flow pointer raster file should be set to the output from the D8 flow pointer tool. In the example the "Output Type" was set to "cells" so that a greater cell value in the output would correspond to a greater number of cells flowing through that cell. The "Log-transform output" box was left unchecked in this example, though checking this would help normalize the data for better display. After these inputs have been set click, run the tool.
[[File:FillDepressions.PNG]]


[[File:FillDepressionsOtp.PNG|800px]]
[[File:D8 accumulation tool.png|600px]]


The output of this tool is displayed below. The brighter areas correspond to areas of higher accumulated flow. These areas of high flow correspond to the areas where more water gathers and flows together. A beter picture of the data can be gathered by zooming into the output in Whitebox.
===Flow Pointer===
[[File:FlowPointer.PNG]]


[[File:FlowPointerMsg.PNG|800px]]
[[File:FlowAccumulationOtp.PNG|600px]]


===Isobasin===
[[File:FlowPointerOtp.PNG|800px]]


The isobasin tool divides a study area into equally sized drainage areas (iso-basins) of a specified size.
===Flow Accumulation===
[[File:FlowAccumulation.PNG]]


The location of this tool is displayed below.
[[File:FlowAccumulationMsg.PNG|800px]]


[[File:FlowAccumulationOtp.PNG|800px]]
[[File:Isobasins tool location.png]]


The dialog box for this tool is displayed below. The input is the original, hydrologically conditioned (depression fill) raster.
===Isobasin===

[[File:Isobasin.PNG]]
[[File:Isobasins tool.png|600px]]


The output from this look is displayed below. It can be seen that the area has been broken down into 11 different basins of approximately equal size. It also appears that the basins do not fill the entire study area. This is likely because no more basins of a size of 500,000 cells could be fit into these areas. If the target basin size was set to a lower number these basins would conform to the study area more completely.
[[File:IsobasinMsg.PNG|800px]]


[[File:IsobasinOtp.PNG|800px]]
[[File:IsobasinOtp.PNG|600px]]


===Extract Streams===
===Extract Streams===
[[File:ExtractStreams.PNG]]


Stream networks can be useful as an input for other tools. Also, on their own they allow knowledge of areas of high water and nutrient flow, as well as connecting areas between water habitats.
[[File:ExtractStreamsMsg.PNG|800px]]


The "Extract Streams" tool was used for this purpose. This tool extracts all values from a flow accumulation output that are greater than the specified value. This tool is part of the "Stream Network Analysis" toolset.
[[File:ExtractStreamsOtp.PNG|800px]]
The location of this tool is displayed below.

[[File:Extract streams tool location.png]]

The dialog box for this tool is displayed below. The input flow-accumulation raster file should be set to the output from the D8 Flow Accumulation (D8 Flow Accumulation). The "Channelization Threshold" is the cutoff value that will be used to determine which cells are a stream and which cells aren't. Trial and error was used to determine a value that produced an appropriate stream network. A value of 5,000 was settled on. Please make sure to check the "If true, non-stream background is 0 instead of NoData" box. This is because later tools in this analysis require rasters without NoData values.

[[File:Extract streams tool.png|600px]]

The output of the tool is displayed below. This output looks patchy at the full extent, but by zooming into it within Whitebox you can confirm that a network of continuous lines has been produced.

[[File:ExtractStreamsOtp.PNG|600px]]


===Sub-basins===
===Sub-basins===
[[File:Subbasins.PNG]]


The sub-basin tool breaks the down the study area into a number of basins, with one basin for each segment of a stream network for the area. As a result each of these basins represent the catchment area for each segment of the river network.
[[File:SubbasinsMsg.PNG|800px]]


The location of this tool is displayed below.
[[File:SubbasinsOtp.PNG|800px]]
<br>


[[File:Subbasins tool location.png]]
===Watershed Analysis===
<br>


The dialog box for this tool is displayed below. The input streams raster file should be set to the output from the extract streams tool, and the input D8 flow pointer raster should be set to the output from the D8 flow pointer tool . After these inputs have been set, run the tool.
<br>

[[File:Subbasins tool.png|600px]]
<br>

The output from this tool is displayed below. This image shows a much greater number of basins than any of the outputs from other tools in this tutorial, likely due to the complexity of the stream network fed into the tool. It would be expected that if the channelization threshold used for the extract streams tool was higher, there would be less sub-basins, and if it was lower there would be more.
<br>

[[File:SubbasinsOtp.PNG|600px]]

===Watershed Analysis===
In order to run the Watershed tool this first step will be to create pour points. Once this is done The watershed analysis can be done.
====Pour Points====
====Pour Points====
Pour points are used in watershed analysis to define each of the watersheds that will be output. Simply put, a watershed is the entire area that flows into a pour point. As a result the placement of these pour points greatly effects the output of the watershed analysis. Pour points are usually located in areas of high accumulated flow, so are usually located on points of a stream network.
[[File:BlankOutletRaster.PNG]]


There is no way to create a pour point file in Whitebox automaticaly, so this must be done manualy. You can do this by creating a new point layer in QGIS. Go to layer > Create layer
[[File:BlankOutletRasterMsg.PNG|800px]]


[[File:ModifyPixelTool.png]]
[[File:Create new layer location.png | 400px]]


You can create whichever data structure you prefer for vectors, for this tutorial we use a shapefile. Make sure to set your CRS to the same CRS as the hydrological products that have already been created. Then set the geometry type to Point. Your dialog box may look something like below.
[[File:ModifyPixelToolUse.png|800px]]


[[File:ModifyPixelToolMsg.png]]
[[File:Create points layer.png | 500px]]


Pour points must now be identified and added. Before this can be done, the layers in the data tab have to be set up. I made sure that only the extract streams output and the create blank outlet raster output were visible.
[[File:SnapPourPoints.PNG]]


Next the vector layer must be set to editing mode, start by enabling editing like so.
[[File:SnapPourPointsMsg.PNG|800px]]


[[File:Toggle editing.png]]
====Watershed====
[[File:Watershed.PNG]]


You can then create points from here by first clicking on the 'Add Point Feature' button
[[File:WatershedMsg.PNG|800px]]


[[File:WatershedOtp.PNG|800px]]
[[File:Add point feature.png]]


After clicking this button your cursor will become a cross-hair when mousing over your data frame. The center of this cross-hair is the location of the pixel that will be altered using this tool.
==Conclusion==
'''''In conclusion, this tutorial was aimed to give the user the skills to create workflows using the QGIS Processing Toolbox while also creating a workshop for slope and terrain analysis. This tutorial also gives the user the very basic introduction into the GIS world of Python scripting as well. The Python scripts that were exported can be slightly edited to preform the same geoprocessing tasks but with different parameters if necessary.
'''''


Click on a location along the stream network, such as the location displayed below. When you click on it a small window like the one below will appear. Give your point an a unique ID so that it can be saved in the vector.
==Resource Links==
[http://docs.qgis.org/2.18/en/docs/index.html QGIS version 2.18 Documentation]


[[File:Place pour point.png|500px]]
[http://www.gdal.org/ GDAL - Geospatial Data Abstraction Library]


Repeat this process until you are happy with the placement of your pour points, making sure that the value of each pour point is unique.
[http://support.esri.com/en/knowledgebase/GISDictionary/term/aspect Aspect - GIS Dictionary]
For the example in this tutorial 10 pour points were spread evenly along the stream network and were given sequential values from 1 to 10.


It is important that the placement of these pour points is on the stream network, so the Jenson Snap Pour Points tool will now be used to make sure that this is true.
[http://support.esri.com/en/knowledgebase/GISDictionary/term/hillshading Hillshade - GIS Dictionary]


The location of this tool is displayed below.
[http://support.esri.com/en/knowledgebase/GISDictionary/term/interpolation Interpolation - GIS Dictionary]


[[File:Jenson snap pour points tool location.png]]
[http://support.esri.com/en/knowledgebase/GISDictionary/term/slope Slope - GIS Dictionary]


The dialog box for this tool is displayed below. The input streams raster should be set to the output from the extract streams tool. After these inputs have been set, run the tool.
[http://learnpythonthehardway.org/ Python - Learn Python the Hard Way]


[[File:Jenson snapped pour points.png | 500px]]
[http://notepad-plus-plus.org/ Notepad++ Homepage]


After this you will get a new point layer that is perfectly snapped to the stream network. Use this point layer for future analysis instead of your manually created layer.
==References==

Crosetto, M., Tarantola, S., & Saltelli, A. (2000). Sensitivity and uncertainty analysis in spatial modelling based on GIS. ''Agriculture, Ecosystems and Environment'', 81(1), 71-79. doi:10.1016/S0167-8809(00)00169-9
====Watershed====

Now that the pour point raster has been created and snapped to the stream network the watershed analysis can be undergone. The location of this tool is displayed below.

[[File:Watersheds tool location.png]]

The dialog box for this tool is displayed below. The D8 flow pointer raster file should be set to the output from the D8 flow pointer tool. The pour point file should be set to the output from the Jenson snap pour points tool. After these inputs have been set, run the tool.

[[File:Watersheds tool.png|600px]]

The output of this tool is displayed below. This shows 10 watershed ares, corresponding to the locations that the pour points were located. Each of these watersheds also conserve the value that its pour point had, meaning that any hierarchy or numbering system will be kept.

The number and location of your watershed areas will differ as a result of the different pour points used.

[[File:WatershedOtp.PNG|600px]]

==Conclusion==


This tutorial aimed to give the user in introduction to hydrological analysis using Whitebox GAT 3.4.0. This was done by taking the user through an organized process that linked many of the hydrology tools together and explained why they were used and how the parameters were decided for each one.
Hutchinson, M.F., 1998. Interpolation of Rainfall Data with Thin Plate Smoothing Splines – Part II: Analysis of Topographic Dependence. ''Journal of Geographic Information and Decision Analysis'', vol.2, no. 2, pp. 152-167, 1998.


The user should now have a good basis of knowledge that will help them with future hydrological analysis in Whitebox Geospatial Analysis Tools.
R.E. Crochiere and L.R. Rabiner. (1983). Multirate Digital Signal Processing. Englewood Cliffs, NJ: Prentice–Hall.

Latest revision as of 14:58, 9 October 2026

Introduction

WhiteBox.png

This tutorial uses Whitebox tools, an open source GIS software that was developed within the Center for Hydrogeomatics in Guelph University. As a result this software package has a heavy focus on hydrological analysis. For this reason Whitebox was chosen for this tutorial on hydrological analysis. WhiteBox has recently been completely re-written from the ground up using a more advanced backend. This means that the toolset has migrated away from a stand-a-lone software. It is now accessible either through code (Python or R) or as a package using QGIS. This tutorial originally used the older version but has been updated to use the QGIS version in October 2026.

The area of focus in this tutorial is Calabogie Ontario. This location was chosen because the Calabogie peak adds some relief to the area, and the author knew it well enough to tell if there were any errors that occurred during the analysis process.

This tutorial uses a single input, a Digital Elevation model, and produces a multitude of outputs from it, adding information that could be used for future analysis. The process that will be undergone in this tutorial is displayed in the image below. To understand the context of each tool used in this tutorial please refer back to this image as needed.

Overview.PNG

Data Acquisition

In this tutorial the only necessary layer is a Digital Elevation Model (DEM) file of your area of interest. In this tutorial we are focusing on Calabogie, ON. It is recommended that you use tthis same dataset for following along.

It can be acquired and downloaded here.

A sample of this data is shown bellow.

DataExa.PNG

For the event that the dropbox link has become inactive the process of obtaining this data is described below to make this tutorial relevant for longer.

Access the Government of Canada Geospatial Data Extraction Application here.

In the “Select Clipping Area” bar enter change the selection to "Predefined Clipping Area" and then select "Drainage areas" from the drop down list that appears.

SelectClipArea.png

This produces a long list of sequential drainage area names. Search through the names until you find "02KE000" and select it. I found this on the 17th page of drainage area names.

The map extent on the right side of the web page should now match the image below.

MapExtent.PNG


Under “Select Data to be extracted” Select “Elevation – Digital elevation model”.

Under “Select options and submit job” fill all of the required boxes so that it matches the figure below. Make sure to enter the email address that you would like to have the file sent to in the “Email Address” field.

SelectOptions2.png

An email will be sent to the entered email address shortly which contains a URL for the direct download of the data.

If neither of these options are available, any DEM raster can be used.

Acquiring and Installing Whitebox Plugin (QGIS)

Please note the previous version of Whitebox used for this tutorial is now deprecated and has transitioned to be used via coding APIs or QGIS only. This tutorial will now use Whitebox Geospatial Analysis Tools in QGIS instead of the older version. This tutorial presumes the user has some QGIS knowledge and already has QGIS installed. For more details, please see the the QGIS download page for more instructions.

To setup your QIGS workspace for WhiteBox you will need to install the "WhiteBox Workflows for QGIS" plugin.

To start, find the plugin manager in QGIS by going to plugins > Manage and Install Plugins...

Plugin installer.png

Then search all plugins for "WhiteBox Workflows for QGIS"

Install Plugin Whitebox.png

Install the plugin, once that is finished please move on to the next section.

Getting Started

Accessing WhiteBox Tools

You're now all set to start using WhiteBox Tools. If you do not see them go to Processing > Toolbox to display the window.

Toolbox location.png

You will find the whitebox tools displayed at the bottom of the list. These tools will be used for the rest of the tutorial so please make sure you have access to them as shown here.

Whitebox in toolkit.png

Import DEM into QGIS

Import the DEM you downloaded into QGIS by adding it as a layer. You can do this by finding the layer in the QGIS browser or simply dragging it from the directory into QGIS. If it correctly imported, you should see the DEM displayed on the screen.

DataExa.PNG

Hydrological Analysis

DEM Pre-Processing

Pre-processing is an important first step in any hydrological analysis as this process identifies and corrects all features within the DEM that may disrupt the flow analysis. Since all products are derived from the DEM it is important to make these corrections at the begging of the process to prevent these errors from carrying through into all of the hydrological outputs.

In this tutorial the "Fill Depressions" tool is used to hydrologically correct the DEM. This was chosen because it is much more computationaly efficient than any of the breach tools, finishing much quicker.

This tool is found in the location below.

Fill depressions tool location.png

The dialog box that appears for this tool is shown below. The input file should be set to the original Calabogie DEM.

Fill depressions tool.png

The output of this tool is shown below. It does not appear very different to the original DEM, but will closer inspection differences within the areas identified in the Find No-Flow Cells output can be seen.

FillDepressionsOtp.PNG

Flow Pointer

A flow pointer tool in Whitebox is a tool that identifies which area surrounding a cell is the lowest. The value of this cell is then assigned corresponding to the relative direction of this area. This information is not too useful on its own, but it is used as an input to many other hydrology tools because it denotes the direction that water will flow from each cell.

Whitebox has many different flow pointer tools that each use a different method to produce their results. In this tutorial "D8 Flow Pointer" was used because many of the tools in the "Watershed Tools" toolset will only work with the output from the D8 Flow Pointer as an input. This tool is found in the location shown below.

D8 flow tool location.png

The dialog box for this too is shown below. The input DEM raster file should be set to the output from the Fill Depressions tool.

D8 flow tool.png

The output from this tool is displayed below. This image contained 8 colours corresponding to the 8 directions of flow. This image appears chaotic, but will be used in other tools to create more informative data products.

FlowPointerOtp.PNG

Flow Accumulation

Flow Accumulation tools analyze the magnitude of cells that pour into or through an area. This is useful on its own, allowing us to determine the relative flow through areas by comparing values of the output, and is also used as an input for many other analyses.

In this tutorial the "D8 Flow Accumulation" tool was used, as this was the one that corresponded to the D8 Flow Pointer output that was created with the previous tool. This tool is located in the location displayed below.

D8 accumulation tool location.png

The dialog box for this tool is displayed below. The input D8 flow pointer raster file should be set to the output from the D8 flow pointer tool. In the example the "Output Type" was set to "cells" so that a greater cell value in the output would correspond to a greater number of cells flowing through that cell. The "Log-transform output" box was left unchecked in this example, though checking this would help normalize the data for better display. After these inputs have been set click, run the tool.

D8 accumulation tool.png

The output of this tool is displayed below. The brighter areas correspond to areas of higher accumulated flow. These areas of high flow correspond to the areas where more water gathers and flows together. A beter picture of the data can be gathered by zooming into the output in Whitebox.

FlowAccumulationOtp.PNG

Isobasin

The isobasin tool divides a study area into equally sized drainage areas (iso-basins) of a specified size.

The location of this tool is displayed below.

Isobasins tool location.png

The dialog box for this tool is displayed below. The input is the original, hydrologically conditioned (depression fill) raster.

Isobasins tool.png

The output from this look is displayed below. It can be seen that the area has been broken down into 11 different basins of approximately equal size. It also appears that the basins do not fill the entire study area. This is likely because no more basins of a size of 500,000 cells could be fit into these areas. If the target basin size was set to a lower number these basins would conform to the study area more completely.

IsobasinOtp.PNG

Extract Streams

Stream networks can be useful as an input for other tools. Also, on their own they allow knowledge of areas of high water and nutrient flow, as well as connecting areas between water habitats.

The "Extract Streams" tool was used for this purpose. This tool extracts all values from a flow accumulation output that are greater than the specified value. This tool is part of the "Stream Network Analysis" toolset. The location of this tool is displayed below.

Extract streams tool location.png

The dialog box for this tool is displayed below. The input flow-accumulation raster file should be set to the output from the D8 Flow Accumulation (D8 Flow Accumulation). The "Channelization Threshold" is the cutoff value that will be used to determine which cells are a stream and which cells aren't. Trial and error was used to determine a value that produced an appropriate stream network. A value of 5,000 was settled on. Please make sure to check the "If true, non-stream background is 0 instead of NoData" box. This is because later tools in this analysis require rasters without NoData values.

Extract streams tool.png

The output of the tool is displayed below. This output looks patchy at the full extent, but by zooming into it within Whitebox you can confirm that a network of continuous lines has been produced.

ExtractStreamsOtp.PNG

Sub-basins

The sub-basin tool breaks the down the study area into a number of basins, with one basin for each segment of a stream network for the area. As a result each of these basins represent the catchment area for each segment of the river network.

The location of this tool is displayed below.

Subbasins tool location.png

The dialog box for this tool is displayed below. The input streams raster file should be set to the output from the extract streams tool, and the input D8 flow pointer raster should be set to the output from the D8 flow pointer tool . After these inputs have been set, run the tool.

Subbasins tool.png

The output from this tool is displayed below. This image shows a much greater number of basins than any of the outputs from other tools in this tutorial, likely due to the complexity of the stream network fed into the tool. It would be expected that if the channelization threshold used for the extract streams tool was higher, there would be less sub-basins, and if it was lower there would be more.

SubbasinsOtp.PNG

Watershed Analysis

In order to run the Watershed tool this first step will be to create pour points. Once this is done The watershed analysis can be done.

Pour Points

Pour points are used in watershed analysis to define each of the watersheds that will be output. Simply put, a watershed is the entire area that flows into a pour point. As a result the placement of these pour points greatly effects the output of the watershed analysis. Pour points are usually located in areas of high accumulated flow, so are usually located on points of a stream network.

There is no way to create a pour point file in Whitebox automaticaly, so this must be done manualy. You can do this by creating a new point layer in QGIS. Go to layer > Create layer

Create new layer location.png

You can create whichever data structure you prefer for vectors, for this tutorial we use a shapefile. Make sure to set your CRS to the same CRS as the hydrological products that have already been created. Then set the geometry type to Point. Your dialog box may look something like below.

Create points layer.png

Pour points must now be identified and added. Before this can be done, the layers in the data tab have to be set up. I made sure that only the extract streams output and the create blank outlet raster output were visible.

Next the vector layer must be set to editing mode, start by enabling editing like so.

Toggle editing.png

You can then create points from here by first clicking on the 'Add Point Feature' button

Add point feature.png

After clicking this button your cursor will become a cross-hair when mousing over your data frame. The center of this cross-hair is the location of the pixel that will be altered using this tool.

Click on a location along the stream network, such as the location displayed below. When you click on it a small window like the one below will appear. Give your point an a unique ID so that it can be saved in the vector.

Place pour point.png

Repeat this process until you are happy with the placement of your pour points, making sure that the value of each pour point is unique. For the example in this tutorial 10 pour points were spread evenly along the stream network and were given sequential values from 1 to 10.

It is important that the placement of these pour points is on the stream network, so the Jenson Snap Pour Points tool will now be used to make sure that this is true.

The location of this tool is displayed below.

Jenson snap pour points tool location.png

The dialog box for this tool is displayed below. The input streams raster should be set to the output from the extract streams tool. After these inputs have been set, run the tool.

Jenson snapped pour points.png

After this you will get a new point layer that is perfectly snapped to the stream network. Use this point layer for future analysis instead of your manually created layer.

Watershed

Now that the pour point raster has been created and snapped to the stream network the watershed analysis can be undergone. The location of this tool is displayed below.

Watersheds tool location.png

The dialog box for this tool is displayed below. The D8 flow pointer raster file should be set to the output from the D8 flow pointer tool. The pour point file should be set to the output from the Jenson snap pour points tool. After these inputs have been set, run the tool.

Watersheds tool.png

The output of this tool is displayed below. This shows 10 watershed ares, corresponding to the locations that the pour points were located. Each of these watersheds also conserve the value that its pour point had, meaning that any hierarchy or numbering system will be kept.

The number and location of your watershed areas will differ as a result of the different pour points used.

WatershedOtp.PNG

Conclusion

This tutorial aimed to give the user in introduction to hydrological analysis using Whitebox GAT 3.4.0. This was done by taking the user through an organized process that linked many of the hydrology tools together and explained why they were used and how the parameters were decided for each one.

The user should now have a good basis of knowledge that will help them with future hydrological analysis in Whitebox Geospatial Analysis Tools.

Retrieved from "https://dges.carleton.ca/CUOSGwiki/index.php?title=Hydrological_Analysis_Using_Whitebox_Geospatial_Analysis_Tools&oldid=24227"